Supersonic chemical transfer laser

ABSTRACT

A laser having a gas generating section that delivers a flow of high pressure high temperature gas which contains a large concentration of active fluorine atoms (F) to a nozzle. This gas is expanded through a nozzle to achieve low pressure low temperature supersonic flow which still contains the large concentration of the active atoms. The nozzle includes one set of injection ports positioned so as to inject cold carbon dioxide gas (CO2) into the flow at a point in the nozzle where the flow is supersonic, just downstream of the throat; and another set positioned so as to inject deuterium (D2) into the flow after the CO2 has mixed with the fluorine containing flow, just at the nozzle exit plane. All gases exhaust from the nozzle into a lasing chamber wherein the energy of F + D2 reaction which initially appears as vibrational energy in the product DF molecule is transferred in collisions to the CO2 molecule. Thus producing a total inversion in the CO2 which allows the energy to be extracted as a laser beam from the flow.

United States Patent [191 Roberts SUPERSONIC CHENflCAL TRANSFER LASERinventor: Thomas G. Roberts, Huntsville, Ala.

Assignee: The United States of America as represented by the Secretaryof the Army, Washington, DC.

Filed: Dec. 4, 1973 Appl. No.: 421,569

Int. Cl. H015 3/09, HOls 3/22 Field of Search 331/945 P, 94.5 G

References Cited UNITED STATES PATENTS 9/1973 Roberts et al. 331/945 PPrimary Examiner-John Kominski Assistant Examiner-Darwin R. HostetterAttorney, Agent, or Firm-Edward J. Kelly; Herbert Berl; Herbert H.Murray 1 Aug. 27, 974

[57] ABSTRACT A laser having a gas generating section that delivers aflow of high pressure high temperature gas which contains a largeconcentration of active fluorine atoms (F) to a nozzle. This gas isexpanded through a nozzle to achieve low pressure low temperaturesupersonic flow which still contains the large concentration of theactive atoms. The nozzle includes one set of injection ports positionedso as to inject cold carbon dioxide gas (CO into the flow at a point inthe nozzle where the flow is supersonic, just downstream of the throat;and another set-positioned so as to inject deuterium (D into the flowafter the CO has mixed with the fluorine containing flow, just at thenozzle exit plane. All gases exhaust from the nozzle into a lasingchamber wherein the energy of F D reaction which initially appears asvibrational energy in the product DF molecule is transferred incollisions to the CO molecule. Thus producing a total inversion in theCO which allows the energy to be extracted as a laser beam from theflow.

SOURCE LASING [CHAMBER is F 2 SOURCE [HOT GAS GEN. /|O 28 I *r- |4 P- II HF 1 l H I l F2 1 4' N u 2 l 26 2 ,24 22 SOURCE SOURCE EIOO EXHAUSTSYSTEM SOURCE SUPERSONIC CHEMICAL TRANSFER LASER BACKGROUND OF THEINVENTION The existing subsonic chemical transfer lasers operated bymixing CO in the plenum where the active atoms are produced. This ispossible because in the lasers the plenum pressure and temperature isnot much different from the pressure and temperature in the opticalcavity and the CO does not chemically react with the active atomconcentration. The otherreactant in the desired reaction is theninjected into this stream of active atoms and CO at or near thebeginning of the optical cavity. For example if the active atoms arefluorine (F) then deuterium or hydrogen may be injected at the opticalcavity. In this case the reaction F D DF* D produces DF* which is in anexcited vibrational state, and since CO is in the vicinity where thereaction takes place then the excited DF* transfers its vibrationalenergy to the upper laser level of CO as follows:

This is a resonant like collisional transfer similar to the transfer ofvibrational energy from nitrogen to CO in the gas dynamic lasers exceptthat here the energy level match is not as close. In this manner a totalpopulation inversion is produced in the CO whereas only a partialinversion is produced in the DF when CO is not used, and sincethe CO canbe pumped by more than just one level of the excited DF* molecule, (itis not necessary for any type of inversion to exist in the DF moleculesin order for an inversion to be produced in CO more laser power perpound of flow can be obtained when these lasers are operated in thetransfer mode. Additional advantages may be achieved if these transferlasers are operated with supersonic flows in the cavity. Because of themore rapid removal of the waste energy much more power can be obtainedand the cavity pressure may be raised to the point where these lasersmay operate without auxiliary power supplies, and bulky, heavy equipmentsuch as vacuum chambers, pumps, and compressors. But, to realize theseadvantages the plenum pressures and temperatures which must be used aresuch that the CO can not be injected into the plenum where the activeatoms are produced without reactions occuring which change the CO toother compounds before it leaves the plenum. Because of this, when anattempt is made to operate the existing supersonic HF or DF chemicallasers as transfer chemical lasers, the CO is injected along with the Hor D into the supersonic flow from the plenum at the nozzle exit whichis also where the optical cavity generally begins. This is usually doneby mounting small needles along the leading edges of the nozzles anddrilling small holes in these needles through which the CO and H areinjected. However, in this configuration the laser does not function asa transfer chemical laser because the H diffuses or mixes into thefluorine stream much faster than does the CO and since there is no COnear where the F H HF H reaction occurs the HF develops a partialinversion and lases before the energy can be transferred to the CO Onemight prevent this lasing by moving the mirrors of the optical cavityfar enough downstream to give the CO time to mix into the stream wherethe HF is located. But, during this time the temperature of the streamwill rise due to the chemical reactions which are taking place and dueto some collisional relaxation of the HF which is very fast compared tothe collisional relaxation of the CO Both of these effects will causethe power available for extraction in the laser beam to decrease and thelaser will operate much less efficiently if at all.

A very good if not the best method for operating a supersonic chemicaltransfer laser would be to first freeze the fluorine from the plenum byrapid aerodynamic expansion to a temperature and pressure Where CO canbe easily mixed into the flow. Then after a short time, say at thenozzle exit, the D or H can be injected. In this configuration CO wouldbe available in the supersonic stream when and where the excited DF* orHF8 is produced. Thus allowing the CO to quench the HF or DF radiationand producing a total population inversion in the CO In thisconfiguration it would also be possible to inject CO along with the H orD if this proves to be desirable.

SUMMARY OF THE INVENTION The object of this invention is to provide asupersonic chemical transfer laser in which the molecule, say CO towhich the energy is to be transferred is made to be at the proper placeat the proper time. The laser consists generally of a plenum or hot gasgenerating section for providing a fairly large concentration of activeatoms, say Fluorine, and a nozzle section that receives the F from thegenerating section and expands it to a supersonic velocity which alsocauses the pressure, and the temperature to drop to low values. Thisexpansion is produced in a time which is short compared to therecombination time of the F atoms so that the F atoms concentrationproduced in the plenum is essentially frozen or retained in the lowpressure, low temperature supersonic flow. The nozzle section includestwo sets of injection ports. One set which is connected to a source ofCO for injecting cold CO into the supersonic flow from the plenum beforeit reaches the nozzle exit plane, and another set which is connected toa source of say D for injecting this gas into the now mixed supersonicflow of F atoms and CO when it reaches the nozzle exit plane. A lasingchamber or optical cavity is connected to the downstream side of thenozzle section and receives the exhaust therefrom. In the lasing chamberthe D stream mixes with the other stream and the flowing reactionoccurs.

DF* CO CO DF b CO2* 2h! CO2 where hv is a photon at 10.6 [1.- Thesephotons consititute most of the radiation flux in the optical cavity ofwhich a fraction L is coupled out into the laser beam.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofthe laser device.

FIG. 2 is an enlarged cross sectional view of the nozzle section andlasing chamber.

FIG. 3 is a cross-section of the nozzle piece illustrating thearrangement of the cooling water and gas passage ways and the injectionports.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings. In FIG.l the laser includes a hot gas generating section 10 that provides aflow which contains a relatively large concentration of F atoms to anozzle section 12 mounted downstream. The gas generator consists of a H+F burner 1.4 which is operated fluorine rich, however, other reactionscould be used or hot N from an electric are or resistance heater couldbe used to dissociate the fluorine. Fluorine gas from a suitable source16 is supplied through conduit 18 to the hot gas burner 14 where it isburned with hydrogen gas from a source 20 through conduit 22. A diluentsuch as N is supplied to the generator chamber 10 from a source 24through a conduit 26. Only part of the fluorine is burned and the energyreleased heats the gas mixture in the plenum to a thermal equilibriumcondition where a large concentration of fluorine atoms exist prior toexpansion through the nozzle section. The nozzle section 12 is mountedto a plenum 28 by bolting or other suitable means. The plenum 28 isconnected to the hot gas generator 10.

The nozzle section as more clearly shown in FIGS. 2 and 3 comprises anelongated nozzle piece 30 that is made in four sections 32, 34, 36, and38 that are stacked for use. When stacked the nozzle forms a pluralityof elongated slits or channels 40 that form supersonic nozzles. (Morenozzles than are shown may be used and it may be desirable to arrangethe nozzles so that the channels run perpendicular to the directionshown.) Each channel, see FIG. 3, consists of a converging section 42that joins a throat section 44 which is terminated by a diverging orexit section 46. The nozzles 32, 34, 36 and 38 are provided withpassageways 50, 52, 54 and 56 respectively which supply CO from source61 through conduit 63 to ports 60, 64, 66, 68, 70 and 72 which introducethe CO to the stream of gas flowing through the nozzles just downstreamof the restricted zone thereof.

Similarly passageways 80, 82, 84 and 86 are provided in nozzles 32, 34,36 and 38 respectively and are connected to the source of D by conduit83. The passageways 80, 82, 84 and 86 are connected by small passageways90, 92, 94 and 96 respectively to the flow stream after it leaves thenozzle at the entrance to the lasing chamber or optical cavity 100.

A series of ports 102, E04, 1106 and 108 in the nozzles 32, 34, 36 and38 are connected to a circulating system for cooling water not shown.

There are as many injection ports used in each of the passageways as inconsistent with the flow rates desired and construction capabilities.The fluorine and the CO are thoroughly mixed in the remaining divergingportion of the nozzle before the D is injected from its ports. As soonas the D diffuses or mixes into the fluorine plus CO flow the reactionsas indicated above take place and lasing on the rotational-vibrationaltransitions of CO develops.

The important thing is that there is a separeate place for injecting theCO and the D and that these are located in the proper locations.Although, the F D DF*, DF* CO CO DF reaction has been used as anillustration other transfers could just as well have been used, eq., F.H HF* H, HF* CO C0 HF; C1 HBr HCl* +Br, HCl* CO CO +l-lCl; F+D DF* +D,DF* N 0 N O* DF, etc. it should also be pointed out that it is notnecessary for the D injectors to be built into the nozzles. These couldbe needles fastened to the leading edge of nozzles or the nozzles couldbe made in two sections with the D injectors being located in thedownstream section and the direction of the injected D streams may beother than that shown.

I claim:

1. A supersonic chemical transfer laser comprising a gas generatorchamber,

a burner in said chamber,

means for supplying fluorine and hydrogen to said burner to provide afluorine rich mixture to said burner,

a plenum chamber to provide intermixing of the products of combustionfrom said burner,

a nozzle section for expanding the gases from said plenum chamber,

means for supplying carbon dioxide to the gas flow through said nozzlejust downstream from the throat of said nozzle,

means for supplying deuterium to said gas flow downstream from the pointat which the carbon dioxide is introduced,

a lasing chamber attached to one end of said nozzle section, and

means for exhausting the gases at the other end of said lasing chamber.

2. A supersonic chemical transfer laser as set forth in claim 1 whereinthe point at which the deuterium is at the exit from said nozzles.

3. A supersonic chemical transfer laser as set forth in claim 2 whereinmeans are provided for introducing a neutral gas such as nitrogen to thecombustion chamber to control the heat of the combustion gas products.

2. A supersonic chemical transfer laser as set forth in claim 1 whereinthe point at which the deuterium is at the exit from said nozzles.
 3. Asupersonic chemical transfer laser as set forth in claim 2 wherein meansare provided for introducing a neutral gas such as nitrogen to thecombustion chamber to control the heat of the combustion gas products.